JPH0812049B2 - Optical displacement measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement amount measuring device for optically measuring a relative displacement amount and displacement direction of an object. Here, the displacement amount of the object includes not only the movement amount of the object but also the deformation amount.

[0002]

2. Description of the Related Art As one of means for optically measuring the displacement amount and displacement direction of an object, there is a so-called speckle method using a speckle pattern. When a rough surface of an object is irradiated with laser light, the laser light is diffusely reflected and interferes with each other to form a speckled pattern. This pattern is called a speckle pattern, and the individual bright spots that make up the speckle pattern are called speckles. The speckle pattern is unique to the shape of the rough surface of the object. JP-A-59-222709
The publication discloses a deformation amount detecting device using this speckle method. In this apparatus, the speckle pattern before and after the deformation of the measurement object is double-exposure photographed, and the speckle photograph obtained is irradiated with laser light to generate a Young fringe image. This Young fringe image is rotated stepwise from 0 to 180 degrees, and the fringe interval data is sampled by the one-dimensional image sensor each time. The fringe spacing data collected at each rotation angle is compared and calculated, and the rotation angle when the fringe spacing data becomes the minimum is obtained. From this minimum fringe spacing data and the rotation angle at that time, the direction and spacing of the Young fringe image are analyzed. Based on the analysis results,
The movement amount and movement direction of the speckle pattern are obtained, and the deformation amount and deformation direction of the measurement object are calculated.

[0003]

In such a conventional apparatus, it is necessary to rotate the Young fringe image by at least 180 degrees in order to collect the fringe interval data, which causes a problem that it takes time to collect the data. . Further, there is a problem that it takes time to compare and calculate the stripe interval data, which is not sufficient in terms of real-time measurable property.

There is also a problem that a rotation drive device and a rotation control device for rotating the Young's fringe image are required, and the whole detection device becomes large.

The present invention has been made in view of the above problems, and an object thereof is to measure a relative displacement amount and displacement direction of an object to be measured in a short period of time, which is excellent in real-time measurable property and is small in size. It is to provide a displacement amount measuring device.

[0006]

In order to achieve the above object, an optical displacement amount measuring apparatus of the present invention comprises a light irradiating means for irradiating a measuring object with light, and a reflection from the measuring object based on the irradiation light. Recording means for receiving light or transmitted light to double-record the image of the measuring object at a predetermined time interval and recording the relative displacement of the measuring object; and an image recorded by irradiating the recording means with coherent light. Reading coherent light projecting means for reading, the deflecting means for deflecting the read image in at least two directions different from each other, the Fourier transforming means for Fourier transforming the read image, and the reading And a detection unit for detecting the change state of the Fourier transform image due to the deflection of the image and obtaining the relative displacement amount between the measurement target and the recording unit.

[0007]

In the optical displacement measuring device of the present invention having the above-mentioned structure, the measuring object which is relatively displaced with respect to the device is irradiated with the light by the light irradiation means, and the transmitted light or the reflected light from the measuring object is recorded. Let the means receive light. The recording means double-records the image of the measurement object at a predetermined time interval and records the relative displacement state between the measurement object and the recording means (or the optical displacement amount measuring device). The recording means is irradiated with coherent light from the coherent light projecting means to read the double-recorded image recorded on the recording means. The deflecting means deflects the read double recording image in at least two directions different from each other. Further, the Fourier transform means performs Fourier transform on the read double recording image to form a Fourier transform image. The Fourier transform image moves in at least two different directions due to the deflection of the read image. By detecting the moving state (change state) of the Fourier transform image by the detecting unit, the relative displacement amount of the measurement target with respect to the recording unit (or the optical displacement amount measuring device) is obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an optical system diagram showing a schematic configuration of an optical displacement measuring device 1 according to a first embodiment of the present invention.
The measurement object 19 to be measured is conveyed by the transport device 18 as shown in FIG.
The sheet is two-dimensionally conveyed and moved along a conveying surface 18a extending at a right angle to the paper surface of the sheet. A part of the laser light from the He-Ne laser device 2 is deflected by an acousto-optic deflector (hereinafter referred to as "deflector") 4 and is irradiated twice on a measurement object 19 at a predetermined time interval. Has been done.
The reflected light of the measurement object 19 based on the twice-irradiated light is respectively reflected by the imaging lens 5 to the ferroelectric liquid crystal spatial light modulator (hereinafter,
An image (speckle pattern) before and after the movement of the measurement object 19 is double-recorded on the light-incident surface of the writing side of the "light modulator" 6). The other part of the laser light from the laser device 2 passes through the reading optical system 9 and is incident on the reading light incident surface of the first light modulator 6, and the image recorded in the light modulator 6 is read. . The read image is deflected by the deflection optical system 12 in two different directions. The read image is also Fourier transformed by the Fourier transform lens 10 to form a Fourier transformed image on the focal plane after the lens. The Fourier transform image changes according to the deflection of the read image. The changed state is detected by the photodiode 13 provided on the focal plane after the lens. The calculation / control device 14 analyzes the Fourier transform image based on the detection result of the photodiode 13, and calculates the movement amount and the movement direction of the measurement object 19 in the predetermined time interval.
The calculation result and the detection result of the photodiode 13 are displayed on the display surface 14A of the calculation / control device 14, respectively. The arithmetic / control device 14 is a deflector driver 15
And the feedback control of the deflection optical system 12 is performed to adjust the detection result of the photodiode 13 to a desired state necessary for Fourier transform image analysis.

The He-Ne laser device 2 is for emitting laser light which is coherent light, and emits laser light in a linearly polarized state. The laser light emitted from the He-Ne laser device 2 enters the half mirror 3. Here, a part of the laser light is reflected and enters the polarizer 4, and the rest is guided to the reading optical system 9.

The acousto-optic deflector 4 is provided with a medium for propagating ultrasonic waves and functions as a diffraction grating for diffracting incident light to generate first-order diffracted light, like acousto-optic deflectors 12X and 12Y described later. Is. The diffraction angle of the generated first-order diffracted light has the property of changing according to the change of the frequency of the ultrasonic wave. Therefore, the deflector 4 deflects the first-order diffracted light reflected by the half mirror 3 and incident on the deflector 4 in an arbitrary direction according to the modulation of the ultrasonic frequency. That is,
The deflector 4 functions as an optical shutter that selectively irradiates the measurement object 19 with the first-order diffracted light by modulating the ultrasonic frequency. A deflector controller 17 is connected to the deflector 4, and the deflector controller 17 controls the timing of irradiating the measurement object 19 with the first-order diffracted light.

FIG. 2 is a sectional view showing the structure of the ferroelectric liquid crystal spatial light modulator 6. A ferroelectric liquid crystal layer (hereinafter referred to as “liquid crystal layer”) 6C is provided between the pair of alignment layers 6A and 6B. On the side of the alignment layer 6A opposite to the liquid crystal layer 6C, a dielectric mirror 6F, an amorphous silicon layer (hereinafter referred to as "a-Si layer") 6E, and a writing side transparent electrode (hereinafter referred to as "electrode") 6D are provided. Is provided. Further, on the side of the alignment layer 6B opposite to the liquid crystal layer 6C, a read side transparent electrode (hereinafter referred to as "electrode") 6G, a glass layer 6H, and an antireflection film 6I are provided. The liquid crystal layer 6
C is a chiral smectic C (S _c ^* ) liquid crystal. The a
The -Si layer 6E is a photoconductor layer and functions as an address material. The writing side transparent electrode 6D defines a writing light incident surface 6S _w , and the antireflection film 6I defines a reading light incident surface 6S _r . A driving voltage and a compensating voltage for writing and erasing are applied in pulses between the pair of electrodes 6D and 6G as described later. As shown in FIG. 1, an optical modulator controller 16 is connected to the optical modulator 6 to control the voltage applied between the electrodes 6D and 6G.

As shown in FIG. 1, the light modulator 6 is arranged so that the writing light incident surface 6S _w (that is, the writing side transparent electrode 6D) is parallel to the carrying surface 18a of the carrying device 18. Has been done. Further, the light emitting diode (LED) 7 is a writing side incident surface 6S _{w of the} optical modulator 6.
Of the liquid crystal layer 6C is used to erase the image already recorded on the liquid crystal layer 6C.

The chiral smectic C (S _c ^* ) liquid crystal layer 6C has a binary stability characteristic in which the spontaneous polarization of molecules is stable in a state in which either of the electrodes 6D and 6G is oriented. When the liquid crystal layer is stable in one of two stable states, an electric field having a value opposite to the direction of spontaneous polarization and having a value equal to or larger than the threshold value E _s peculiar to the liquid crystal layer is applied to the liquid crystal layer. Then, the spontaneous polarization is inverted so as to be aligned with the direction of the electric field, and the alignment state of the liquid crystal molecules is changed to enter another stable state.

The write operation of the optical modulator 6 will be described below. When the entire liquid crystal molecule is stable with its spontaneous polarization in the direction of one of the electrodes, a DC drive voltage for writing is applied between both electrodes that gives an electric field in the opposite direction of the spontaneous polarization. To do. When the writing pattern light enters the a-Si layer 6E, which is a photoconductor layer, through the incident surface 6S _w , the a-Si layer 6E has a low resistance at the light incident position, and the threshold electric field E _s is generated at the corresponding position of the liquid crystal layer. The above electric field is applied. As a result, the spontaneous polarization of the molecules at the position of the liquid crystal layer corresponding to the light incident portion is inverted in the direction of the electric field, the arrangement state of the molecules is changed, and the writing pattern is changed to the liquid crystal layer 6C.
Will be recorded in. Since this molecular alignment state is retained as it is even after the electric field is cut off, the write pattern is recorded and retained in the liquid crystal layer 6C.

The pattern read operation from the optical modulator 6 on which pattern writing has been performed is performed as follows. In the liquid crystal layer 6C, the alignment state of the liquid crystal molecules is different between the pattern writing position and the other positions, and the refractive index for the reading light is different. Therefore, when the reading light enters from the reading light incident surface 6S _r and propagates in the liquid crystal layer 6C, phase modulation based on the writing pattern is performed, and thus the writing pattern is read.

The readout optical system 9 guides the laser beam transmitted through the half mirror 3 to the readout side of the optical modulator 6 as readout light. In the reading optical system 9, the light transmitted through the half mirror 3 is converted into parallel light having a constant beam diameter by the conversion optical system 8. The conversion optical system 8 includes a pair of collimator lenses 8A and 8C and a spatial filter 8B provided therebetween.
It consists of and. The obtained parallel light is reflected by the mirror 9A and its beam diameter can be changed to a desired value by the variable aperture 9B. This light beam is selectively applied to the half mirror 9D by the shutter 9C. A part of the light beam with which the half mirror 9D is irradiated is reflected and is incident on the read light incident surface 6S _r of the light modulator 6.

The read light incident on the optical modulator 6 is
Read-out light incident surface 6S after being phase-modulated in the liquid crystal layer 6C
_Emit from _r . The emitted read-out light passes through the half mirror 9D and reaches the Fourier transform lens 10. The read light passes through the Fourier transform lens 10 and then enters a deflection optical system 12 described later. The read light is deflected by the deflection optical system 12 and then the Fourier transform lens 10
After reaching the rear focal plane (Fourier transform plane), a Fourier transform image of the read light is formed on the rear focal plane.

The deflection optical system 12 comprises a pair of acousto-optic deflectors 12X and 12Y and a half-wave plate 11 provided therebetween. As shown in FIG. 4A, the acousto-optic deflector 12X is provided with a piezoelectric vibrator (transducer) 122 at one end of a crystal 121 functioning as an ultrasonic propagation medium and an ultrasonic absorber 123 at the other end. The deflector driver 15 shown in FIG. 1 is connected to the piezoelectric vibrator 122 and vibrates it to generate ultrasonic waves. The ultrasonic waves travel inside the crystal 121 from the oscillator 122 to the absorber 123. The crystal 121 during ultrasonic wave propagation functions as a diffraction grating that diffracts the light incident from the incident surface 121a and emits only the first-order diffracted light from the emission surface 121b. Here, the refractive index of the crystal 121 is n, the ultrasonic frequency (frequency of the piezoelectric vibrator) is f, the propagation velocity of the ultrasonic wave is v, and the wavelength of the incident light in vacuum is λ _0.
Then, the diffraction angle θ of the first-order diffracted light is given by Equation 1 below.

[0020]

## EQU1 ## θ = fλ ₀ / nv

When the ultrasonic frequency f is changed by Δf,
The diffraction angle (deflection angle) θ changes by Δθ (= Δfλ ₀ / nv). Therefore, the deflector driver 15 can change the diffraction angle θ by changing the frequency of the piezoelectric vibrator 122, that is, the ultrasonic frequency f. The deflector 12X has a function of deflecting the incident light at the deflection angle θ as described above, and the deflection angle θ can be changed by changing the ultrasonic frequency. Although the deflector 12X has been described above, the deflector 12Y also includes the deflector 12X.
It has the same configuration as X and performs the same operation. Deflector 1
2Y is also connected to the deflector driver 15.

As shown in FIG. 1, deflectors 12X and 12Y are provided.
Is arranged so that the light from the conversion lens 10 can first enter the deflector 12X and the first-order diffracted light can enter the deflector 12Y. For example, the optical axis of the lens 10 is the deflector 1
It is arranged so as to penetrate both the incident surfaces 121a of 2X and 12Y. Here, as shown in FIG. 4A, the axis of the deflector 12X (hereinafter, referred to as "X axis") is set parallel to the vibration direction of the piezoelectric vibrator 121 of the deflector 12X, that is, the traveling direction of the generated ultrasonic waves. Diffraction (or deflection) of incident light is shown in FIG.
As shown in, a plane including the X axis of the deflector 12X and also including the traveling direction of the incident light (hereinafter, referred to as “deflection surface S _X ”).
It is done according to. When the ultrasonic frequency of the deflector 12X is f _X , the deflection angle θ _X is given by the following formula 2. Similarly, the deflector 12Y is moved in the traveling direction of the ultrasonic wave of the deflector 12Y.
Axis (hereinafter referred to as "Y-axis"). As shown in FIG. 4B, when the first-order diffracted light from the deflector 12X is incident on the deflector 12Y, a plane including the traveling direction of the first-order diffracted light and also including the Y-axis (hereinafter, referred to as “deflection surface S _Y ”). Deflected along. When the ultrasonic frequency of the deflector 12Y is f _Y , the deflection angle θ _Y is given by Equation 3. (Note that the deflector 12
The X and 12Y ultrasonic wave propagation media 121 both have the same refractive index n, and the ultrasonic waves propagate at the same velocity v. Therefore, as shown in FIG. 4B, the light from the conversion lens 10 is first deflected by the deflector 12X on the deflection surface S _X at a deflection angle θ _X , and then by the deflector 12Y on the deflection surface S _{Y. Y}
Is biased at.

[0023]

## EQU2 ## θ _X = f _X λ ₀ / nv

[0024]

(3) θ _Y = f _Y λ ₀ / nv

When the ultrasonic frequency f _X of the deflector 12X is changed at a constant rate df _X / dt (that is, sweeping is performed at a constant sweep speed), the deflection angle θ _X is constant at a rate d.
It changes with θ _X / dt. Here, the constant ratio dθ _X / dt is given by Equation 4 below. Therefore, the light from the conversion lens 10 gradually moves on the deflection surface S _X. When the ultrasonic frequency f _Y of the deflector 12Y is swept at a constant sweep speed df _Y / dt,
The deflection angle θ _Y changes at a constant rate dθ _Y / dt. Here, the constant ratio dθ _Y / dt is given by Equation 5 below. Therefore, the light from the deflector 12Y gradually moves on the deflection surface S _Y.

[0026]

## EQU4 ## dθ _X / dt = (df _X / dt) λ ₀ / nv

[0027]

[Number 5] _{dθ Y / dt = (df Y} / dt) · λ 0 / nv

The deflectors 12X and 12Y are shown in FIGS.
As shown in C, the X axis and the Y axis are arranged so as to form an angle of 90 degrees with each other. For example, as shown in FIG. 1, the X axis extends in the direction of FIG. 1 and the Y axis extends in the direction perpendicular to the plane of FIG. X like this
Since the axis and the Y-axis are arranged so as to form an angle of 90 degrees with each other, the deflection surface S _X and the deflection surface S _Y also form an angle of 90 degrees with each other as shown in FIG. 4B. The light from the transform lens 10 is deflected by an angle theta _X is first along a deflecting surface S _X, is deflected by an angle theta _Y along the deflection surface S _Y forming a deflection surface S _X 90 °. Therefore, the light from the conversion lens 10 is deflected by the pair of deflectors 12X and 12Y in two different directions, that is, the angle θ _{X in the X} axis direction and the angle θ _{Y in the} Y axis direction.

The deflection characteristics of the deflector differ depending on the polarization state (polarization direction) of incident light. Polarizer 12X
And 12Y are arranged so that their axial directions form 90 degrees as described above. When light with the same polarization state enters both deflectors, the polarization states of the light with respect to both deflectors will differ from each other, so that both polarization planes S _X and S _{Y of} that light will change.
The characteristics of the deflection along with each other are different from each other. Therefore,
In the present invention, a half-wave plate (λ / 2 plate) 11 is provided between the deflectors 12X and 12Y. The half-wave plate 11 has a function of rotating the polarization direction of the first-order diffracted light emitted from the deflector 12X by 90 degrees and thereafter making it enter the deflector 12Y. The half-wave plate 11 thus matches the polarization state of light with respect to the deflector 12X and the polarization state of light with respect to the polarizer 12Y. As a result, the light from the conversion lens 10 is deflected by the pair of polarizers 12X and 12Y in two mutually different directions (X-axis direction and Y-axis direction) with the same deflection characteristics.

As shown in FIGS. 1 and 4C, the deflector 12
A photodiode 13 is provided on the rear focal plane of the conversion lens 10 on the rear side of Y. Specifically, the light-receiving surface 13a of the photodiode 13 is arranged on the rear focal plane of the conversion lens 10 and at a position where the first-order diffracted light from the deflector 12Y can enter. That is, as shown in FIGS. 4C and 4D, the photodiode 13 has a light-receiving surface 13a which is the exit surface 121b of the deflector 12X and the deflector 12Y.
Is arranged so as to face a range in which the light emitting surface 121b and the light emitting surface 121b overlap. For example, as shown in FIG. 4C, the deflector 12
The optical axes of the lens 10 and X and 12Y are the incident surfaces 121 on both sides.
When it is arranged so as to pass through a, the photodiode 13 may also be arranged on the optical axis of the lens 10. The photodiode 13 has a function of converting the light intensity of the first-order diffracted light emitted from the deflector 12Y that reaches the photodiode light receiving surface position into an electric signal. By the way, on the rear focal plane (Fourier transform plane) of the transform lens 10, the optical modulator 6
A Fourier-transformed image of the light read from the and which is deflected by the deflection optical system 12 is formed. The light receiving surface 13a of the photodiode 13 is arranged at a specific point on the back focal plane of the lens 10 as described above. Therefore, the photodiode 13 detects the state (light intensity) at the specific one point position of the Fourier transform image.

The photodiode 13 converts the light intensity at the specific one point position of the Fourier transform image into an electric signal and outputs the electric signal to the arithmetic and control unit 14 shown in FIG. The arithmetic / control device 14 detects a temporal change of the electric signal from the photodiode 13 (that is, the light intensity at one point position of the Fourier transform image). The arithmetic / control device 14 displays the temporal change state of the electric signal of the photodiode 13 as the detection result on the display surface 14A. The arithmetic / control device 14 also controls the deflector driver 15 based on the detection result to control the ultrasonic frequency f of the deflectors 12X and 12Y.
Adjust _X and f _Y to obtain the desired detection result. That is, the electric signal from the photodiode 13 is set to a desired temporal change state. The calculation / control device 14 calculates the moving amount, moving direction, and moving speed of the measuring object 19 based on the desired detection result obtained as a result of such control and the control content of the deflector driver 15. , The calculation result is displayed on the display surface 14A.

Next, the operation of the optical displacement measuring device 1 according to the above embodiment will be described.

As shown in FIG. 3, while the light of the erasing light emitting diode 7 is applied to the entire light incident surface 6S _w of the optical modulator 6, the erasing DC drive voltage V _e is applied to the electrode 6D of the optical modulator 6.
And 6G. Then, the erasing electric field E _e applied to the liquid crystal layer 6C becomes equal to or higher than the threshold electric field E _s, and the spontaneous polarization of the entire liquid crystal layer molecules is uniformly arranged in the direction of the electric field E _e . As a result, the already recorded image is erased. In order to prevent deterioration of the liquid crystal, a DC compensation voltage V _ec having a polarity opposite to that of the erasing voltage is applied for the same period of time before the erasing driving voltage V _e is applied.

Of the laser beam emitted from the He-Ne laser device 2, the laser beam reflected by the half mirror 3 enters the deflector 4. Under the control of the deflector controller 17, the deflector 4 deflects the first-order diffracted light having a desired spot diameter at a certain time t in a constant deflection direction and irradiates the surface of the measurement object 19. The irradiated light is reflected by the surface of the measurement object 19 and reaches the imaging lens 5. The image forming lens 5 forms an image of the reflected light on the writing light incident surface 6S _w of the light modulator 6 and forms a speckle pattern there.

As shown in FIG. 3, at the time when the speckle pattern is incident on the optical modulator 6, that is, at time t, the writing DC drive voltage V _w is applied between the electrodes 6D and 6G. There is. The write DC drive voltage V _w has a polarity opposite to that of the erase drive voltage V _e . Liquid crystal layer 6
In C, only the electric field E _w at the position corresponding to the position where the bright speckled speckles are incident becomes the threshold electric field E _s or more, and the spontaneous polarization of the molecules at that position is aligned with the writing electric field E _w. Invert. As a result, the alignment state of the liquid crystal molecules at the speckle position changes, and the changed state is recorded. In this way, the speckle pattern image (speckle pattern 1) of the measurement object 19 at time t is recorded and held on the liquid crystal layer 6C. In order to prevent deterioration of the liquid crystal, a compensation voltage V _{wc having a} polarity opposite to that of the drive voltage V _{w for the} same time as the application time before the write drive voltage V _{w is} applied.
Is applied.

Since the ferroelectric liquid crystal spatial light modulator 6 used in this embodiment is a binary recording element having two stable states of liquid crystal molecule alignment as described above, it records a speckle pattern which is a light-dark pattern. Very suitable to do. Further, since the writing speed of the ferroelectric liquid crystal is extremely fast on the order of μsec, it is also excellent in terms of real-time measurable property.

As shown in FIG. 3, the deflector 4 irradiates the measuring object 19 again with light after Δt has elapsed from time t. That is, at time t + Δt, the deflector 4 deflects the first-order diffracted light in the same direction as the deflection direction at time t and irradiates the measurement object 19 with the deflected light. The speckle pattern (speckle pattern 2) obtained by this irradiation is applied to the optical modulator 6 to which the writing drive voltage _Vw is still applied and recorded. Since the liquid crystal layer 6C of the light modulator 6 has a function of holding the recorded information as described above, the speckle patterns 1 and 2 are double-recorded in the liquid crystal layer 6C.

Assuming that the measurement object 19 has moved by ΔS between time t and Δt, the optical modulator 6 will receive time t.
The speckle patterns before and after the movement of the measuring object 19 that has moved within Δt seconds are recorded in double. Since the speckle pattern is unique to the shape of the measurement object 19, etc.,
The speckle patterns 1 and 2 have the same speckle distribution. Therefore, the same speckle pattern is recorded on the liquid crystal layer 6C in a direction parallel to the moving direction of the measurement object 19 with a constant gap ΔN. It should be noted that the shift amount ΔN and the movement amount ΔS of the measurement object 19 have the relationship of the following mathematical expression 6.

[0039]

[Equation 6] ΔN = M · ΔS

In Equation 6, M is a proportional constant determined by the image forming system such as the image forming lens 5.

The double speckle pattern recorded in the liquid crystal layer 6C of the light modulator 6 as described above is read out and optically processed as described below, so that the measured object 1
9 movement amount ΔS, movement direction, and movement speed V if necessary
= ΔS / Δt is obtained.

Of the laser light emitted from the laser device 2, the light transmitted through the half mirror 3 and reflected by the mirror 9A is
The light is guided to the reading optical system 9 and used as the reading light of the optical modulator 6. The beam diameter of the reading light is set to a desired beam diameter by the variable aperture 9B. The reading light is guided to the optical modulator 6 by opening the shutter 9C at the timing shown in FIG. The read light is incident on the read light incident surface 6S _r of the optical modulator 6 and enters the liquid crystal layer 6C.
The liquid crystal layer 6 propagates inside and is reflected by the dielectric mirror 6F.
After propagating in C, the light is emitted from the read light incident surface 6S _r . The read light is phase-modulated and diffracted by the speckle patterns 1 and 2 when propagating in the liquid crystal layer 6C.
Since the read-out light is coherent light, diffracted lights generated by the corresponding speckles of the speckle patterns 1 and 2 interfere with each other to form a bright and dark interference pattern.
This interference pattern corresponds to the distance of the speckles corresponding to each of the speckle patterns 1 and 2, that is, the shift amount ΔN of the speckle pattern. Therefore, the double speckle pattern is read by emitting the interference pattern from the optical modulator 6.

The read interference pattern light due to the double speckle is imaged on the focal plane after the lens by the Fourier transform lens 10. That is, interference fringes (hereinafter referred to as “Young fringes”) as a Fraunhofer diffraction image on the back focal plane.
Image). In other words, the double speckle pattern is Fourier transformed into the spatial frequency domain to form Young fringes on the Fourier transform plane. The direction in which these Young stripes are arranged (the direction perpendicular to the stripes) is the speckle pattern 1
And the deviation direction of 2 (the moving direction of the measurement object 19), and the Young fringe interval (the distance between the bright lines of the Young fringes in the direction perpendicular to the Young fringes) ΔL is the deviation amount ΔN of the speckle pattern and the following Equation 7 Have a relationship.

[0044]

[Formula 7] ΔN = λ ₀ · ι / ΔL

In Equation 7, λ ₀ is the read light (He-N
e is the wavelength of the laser light from the laser device 2 in the air, and ι is the focal length of the conversion lens 10. Therefore, if the direction of Young fringes and the interval ΔL are obtained, the above equations 6 and 7 can be obtained.
The moving direction and the moving amount ΔS of the measurement object are obtained from the above.

On the other hand, in the area before reaching the back focal plane of the lens 10, bright and dark interference fringes are formed as a Fresnel diffraction image by the interference pattern light from the optical modulator 6. That is,
When the Fresnel diffraction image reaches the back focal plane of the lens 10, the Young fringes as the Fraunhofer diffraction image are formed on the plane. Since the deflectors 12X and 12Y are arranged between the lens 10 and the focal plane thereafter, the Fresnel diffraction image is incident on these deflectors. That is, the Fresnel diffraction image first enters the deflector 12X and is deflected along the deflection surface S _X in the X-axis direction. Here, when the ultrasonic frequency f _X of the deflector 12X is swept at a constant sweep speed, the Fresnel diffraction image is gradually deflected along the X-axis direction. The Fresnel diffraction image deflected by the deflector 12X then enters the deflector 12Y and is deflected along the deflection surface S _Y in the Y-axis direction. Here, the deflector 1
When the ultrasonic frequency f _Y of 2Y is swept at a constant sweep speed, the Fresnel diffraction image is gradually deflected along the Y-axis direction.
R> Get going. As a result of the Fresnel diffraction image being gradually deflected along the X-axis and Y-axis directions in this way, Young fringes formed by forming the Fresnel diffraction image form on the focal plane after the lens on the X-axis and Y-axis. It will gradually move in a direction parallel to the direction.

As described above, the light-receiving surface of the photodiode 13 is the deflectors 12X and 12X on the focal plane after the lens.
It is arranged at a position facing the overlapping range of the Y emission surface 121b. Therefore, as a result of the movement of the Young fringes on the back focal plane, the light lines and the dark lines of the Young fringes alternately reach the photodiode light receiving surface, and the output level of the photodiode 13 changes with the passage of time. To do. The calculation / control device 14 measures the time variation of the output level of the photodiode 13, and calculates the fringe spacing and the fringe direction of the Young fringes from this measurement result. Further, the calculation / control device 14 calculates the moving direction and moving amount of the measuring object 19 and, if necessary, the moving speed on the basis of the calculation result.

The method for obtaining the direction of Young fringes and the fringe spacing ΔL by deflecting the Fresnel diffraction image will be described in more detail below.

The deflector driver 15 first detects the deflector 12
The ultrasonic frequency f _X of the deflector 12X is swept at a constant sweep speed df _X / dt while stopping the propagation of the ultrasonic wave to Y or maintaining the ultrasonic frequency f _Y constant. The deflection angle of the deflector 12X is a constant ratio dθ _X / dt
Changes. Here, the constant ratio dθ _X / dt is given by the above-mentioned formula 4. Therefore, the Fresnel interference fringes incident on the deflector 12X are gradually deflected along the deflection surface S _X (X axis) at a constant deflection angular velocity dθ _X / dt. As a result, Young's fringes formed by forming the Fresnel diffraction image on the back focal plane of the conversion lens 10 have a substantially constant velocity v _X in the direction parallel to the X axis (direction toward the deflection surface S _X ). Move on. Here, the velocity v _X is given by the following Equation 8.

[0050]

[Formula 8] v _X = ι _X · d θ _X / dt

Here, ι _X is from the deflector 12X to the lens 1
0 is the distance to the back focal plane. FIG. 5A shows how the bright lines of the Young's fringes move at the speed v _X in the direction parallel to the X-axis direction based on the operation of the deflector 12X. That is, FIG. 5A shows that the Young fringe bright line located at the position indicated by the dotted line has moved to the position indicated by the solid line at the speed v _X.

According to the movement of the Young fringes, when the bright line reaches the light receiving surface 13a of the photodiode 13, the photodiode light receiving intensity increases, and when the dark line reaches, the photodiode light receiving intensity decreases. Therefore, the output level of the photodiode 13 reaches a peak each time the bright line of the Young's fringes is incident on the light receiving surface of the photodiode. According to the ultrasonic frequency sweep of the deflector 12X, Young fringes are shown in FIG.
As a result of the movement as shown in A, the photodiode output level reaches a peak at a constant time interval ΔT _X as shown in FIG. 5B. That is, as a result of the Young fringes moving in the direction parallel to the X axis at a velocity v _X (= ι _X · dθ _X / dt), the bright lines of the Young fringes reach a predetermined photodiode position with a time interval ΔT _X. To do. Therefore, the distance between the bright lines of the Young fringes in the X-axis direction, that is, the fringe spacing ΔL _{X in the} X-axis direction is given by the following formula 9. The ultrasonic frequency sweep speed df _X / dt of the deflector 12X adjusted by the deflector driver 15 is calculated.
It is recorded in the controller 14. The arithmetic / control device 14 also measures the output value of the photodiode 13 and measures the time interval ΔT _X of the output peak. The calculation / control device 14 calculates the stripe interval ΔL _X in the X-axis direction from the sweep speed recording result df _X / dt and the output peak interval measurement result T _{X according} to the following formula 9.

[0053]

[Formula 9] ΔL _X = v _X · ΔT _X = ΔT _X · ι _X · d θ _X / dt = ΔT _X · ι _X · (df _X / dt) · (λ ₀ / nv)

By the way, the arithmetic / control unit 14 is shown in FIG.
As shown in, the maximum time range T _{max in} which the time change of the photodiode output value can be measured, that is, the display surface 14A.
There is a certain limit on the maximum time range that can be displayed above. Here, if the ultrasonic frequency sweep speed df _X / dt is too small compared to the X-axis direction fringe spacing ΔL _X of the Young fringes, the output peak time interval ΔT _{X of the} photodiode 13 exceeds the time limit range T _max . Will grow bigger. In this case, no output peak is displayed or only one output peak is displayed on the display surface 14A, so that it becomes impossible to measure the peak-to-peak time interval ΔT _x .
Therefore, the arithmetic / control device 14 determines whether or not two or more output peaks appear within the time limit range. If it is determined that the output peaks do not appear, the deflector driver 15 is controlled to control the ultrasonic frequency. Increase the sweep speed df _X / dt. In this way, at least two output level peak values of the photodiode 13 are displayed on the display surface 14A, and the fringe spacing ΔL _X of the Young fringes in the X-axis direction is measured. On the other hand, when the ultrasonic frequency sweep speed df _X / dt is too large, the peak time interval ΔT _X becomes smaller than the measurement time accuracy of the arithmetic / control unit 14 and the measurement becomes impossible.
Therefore, the calculation / control device 14 determines whether or not the peak time interval is equal to or greater than a certain minimum limit value T _min . If it is determined that the value is the minimum limit value T _min or less, the calculation / control device 1
Reference numeral 4 controls the deflector driver 15 to decrease the ultrasonic frequency sweep speed df _X / dt and set the peak-to-peak time interval ΔT _X to a measurable value (value equal to or more than the limit value) in the X-axis direction of the Young fringe. Measure the fringe spacing. As described above, the arithmetic / control device 14 controls the ultrasonic frequency sweep speed of the deflector 12X so that the peak time interval ΔT _X is equal to or less than the time limit range T _max of the arithmetic / control device 14 and the minimum limit. After setting the value to T _min or more so that measurement is possible, the stripe interval Δ
L _X is measured.

Next, deflector 12X to either stop the propagating ultrasound or the ultrasonic frequency f _X while keeping constant, the deflector 12Y the ultrasonic frequency f _Y a constant sweep rate df _Y Sweep at / dt. As a result, the deflector 1
The deflection angle θ _{Y of} 2Y changes at a constant ratio dθ _Y / dt.
The dθ _Y / dt is given by Equation 5 described above. Therefore, the Fresnel interference fringes incident on the deflector 12Y are reflected by the deflection surface S
It is gradually deflected along _Y (Y axis) at a constant deflection angular velocity dθ _Y / dt. As a result, as shown in FIG. 5C, Young's fringes formed by forming the Fresnel diffraction image on the back focal plane of the conversion lens 10 are substantially in the direction parallel to the Y axis (the direction toward the deflection surface S _Y ). It moves at a constant speed v _Y. Note that FIG. 5C shows that the Young fringe bright line located at the position indicated by the dotted line has moved to the position indicated by the solid line at the speed v _Y. The velocity v _Y is given by the following mathematical formula 10.

[0056]

[Formula 10] v _Y = ι _Y · d θ _Y / dt

Here, ι _Y is the distance from the deflector 12Y to the back focal plane.

As a result of the Young fringes moving as shown in FIG. 5C in accordance with the ultrasonic frequency sweep of the deflector 12Y, the photodiode output level reaches a peak at a constant time interval ΔT _Y as shown in FIG. 5D. It will be. That is, as a result of the Young fringes moving in the direction parallel to the Y-axis at the velocity v _Y (= ι _Y · dθ _Y / dt), the bright lines of the Young fringes reach the predetermined photodiode position with a time interval ΔT _Y. To do. Therefore, the distance between the bright lines in the Y-axis direction of the Young fringes, that is, the fringe spacing ΔL _{Y in the} Y-axis direction is expressed by the following formula 11
Will be given in.

[0059]

[Formula 11] ΔL _Y = v _Y · ΔT _Y = ΔT _Y · ι _Y · d θ _Y / dt = ΔT _Y · ι _Y · (df _Y / dt) · (λ ₀ / nv)

The arithmetic / control device 14 records the ultrasonic frequency sweep speed df _Y / dt of the deflector 12Y adjusted by the deflector driver 15, and measures the output value of the photodiode 13 to measure the output peak time. Interval ΔT _Y
To measure. The calculation / control device 14 calculates the stripe interval ΔL _Y in the Y-axis direction from the sweep speed recording result df _Y / dt and the output peak interval measurement result ΔT _{Y according} to the above formula 11. Note that, similarly to the case of measuring the output peak interval ΔT _{X in} the X-axis direction, the calculation / control device 14 controls the deflector driver 15 also in the measurement of the output peak interval ΔT _Y. That is, the arithmetic / control device 14 adjusts the ultrasonic frequency sweep speed of the deflector 12Y, obtains a desired time-dependent change of the photodiode output value capable of measuring the output peak interval ΔT _Y , and then performs the measurement. . Specifically, the deflector 12Y of adjusting the ultrasonic frequency sweep rate, the maximum time limits range T _{m ax} the minimum threshold value or less T _min of the peak time interval [Delta] T _Y arithmetic and control unit 14 After setting the measurement conditions as described above, the stripe interval ΔL _Y
Is measured.

[0061] arithmetic and control unit 14 further in this way obtained X-axis direction of the fringe spacing [Delta] L _X and Y-axis direction between [Delta] L (direction perpendicular to the stripes of the Young fringes than fringe spacing [Delta] L _Y Young fringes The distance between the bright lines between stripes and the stripe direction angle ψ (the angle formed by the direction perpendicular to the stripe with respect to the direction parallel to the X axis) are calculated. That is, as shown in FIG. 6, Young fringe spacing Δ
Since L and the intervals ΔL _X and ΔL _Y have the relationship shown in the following formula 12, this formula is calculated to obtain the Young fringe interval ΔL.

[0062]

## EQU12 ## 1 / ΔL ² = 1 / ΔL _X ² + 1 / ΔL _Y ²

Further, the stripe direction ψ is calculated by Expression 13.

[0064]

(13) ψ = tan ⁻¹ (ΔL _X / ΔL _Y ).

As described above, the moving amount ΔS of the measuring object 19 is calculated from the Young fringe spacing ΔL by the following equation (14). Further, the stripe direction angle ψ is X of the measurement object 19.
The moving direction with respect to the direction parallel to the axial direction is shown. For example, as shown in FIG. 1, when the X-axis direction (the axis of the deflector 12X) extends in the direction along the paper surface of FIG.
It can be seen that 9 moves on the conveying surface 18a of the conveying device 18 in a direction forming an angle ψ with respect to the direction along the paper surface of FIG. 1 (X-axis direction).

[0066]

[Expression 14] ΔS = ΔN / M = (λ ₀ · ι) / (ΔL · M)

The measurement of the moving amount and the moving speed of the measuring object 19 described in detail above is performed at the timing shown in FIG. First, a compensating voltage V _ec for erasing and a driving voltage V _e are applied to the first optical modulator 6 in this order while irradiating with the erasing light emitting diode 7. Next, the compensating voltage V for writing is applied to the optical modulator 6.
_{After wc} is added, the write drive voltage V _w is applied. At time t when the write drive voltage V _{w is being} applied, the deflector 4 changes by Δ.
The speckle pattern is double-recorded on the optical modulator 6 by irradiating the measurement object 19 with laser light twice at an interval of t. Simultaneously with the completion of double recording, the shutter 9C is opened to irradiate the optical modulator 6 with read light. After that, calculate
The control device 14 causes the deflector 1 to operate via the deflector driver 15.
2X ultrasonic frequency sweep control is performed to obtain Young fringe spacing ΔL _X in the X-axis direction. Then, ultrasonic frequency sweep control of the deflector 12Y is performed to obtain the Young fringe spacing ΔL _Y in the Y-axis direction. Based on the calculated ΔL _X and ΔL _Y , the calculation / control device 14 further calculates the Young fringe spacing ΔL and the fringe direction ψ. Based on the calculation result, the calculation / control device 14 further calculates the movement amount ΔS and the movement direction of the measurement object 19 at the time interval Δt at the time t. Arithmetic / control device 14
Is the moving speed V (= ΔS / Δ
t) can also be calculated. When the movement amount measurement at the time t is completed in this way, the movement amount ΔS ′ at the time interval Δt ′ is measured by performing the same operation again at the desired time t ′, and the movement speed V ′ at the time t ′. (= ΔS ′ / Δt ′) can also be obtained.

As a method of sweeping the ultrasonic frequency of the deflector for obtaining the Young fringe interval ΔL, as described above, the one of the deflectors is stopped while the frequency sweep is stopped, and the other is as follows. There is such a method.

First, in the same manner as the above-mentioned method, the deflector 12Y is used.
The ultrasonic wave frequency is stopped or the ultrasonic frequency f _Y is kept constant, and the frequency of the deflector 12X is swept at the sweep speed df _X / dt to set the Young fringe spacing ΔL _x in the X-axis direction. Ask. Next, the frequency of the deflector 12X is swept at the sweep speed df _X '/ dt, and the frequency of the deflector 12Y is also swept at the sweep speed df _Y / dt. here,
The sweep speed df _X '/ dt may or may not be equal to the sweep speed df _X / dt. In this case, the Fresnel diffraction image shows the angular velocity dθ in the direction parallel to the X axis by the deflector 12X.
_{X '/ dt (= (df} X' / dt) · λ 0 / nv) simultaneously gradually deflected by deflector angular velocity in a direction parallel to the Y-axis by _{12Y dθ Y / dt (= (} df Y / dt) ・ λ ₀
/ Nv) is gradually deflected. In this way, the Fresnel diffraction image is simultaneously deflected by both the deflectors 12X and 12Y, and as a result, the Young fringes formed by the Fresnel diffraction image are formed in the direction | v _X '| (= Ι _X・ d
θ _X '/ dt) and the velocity in the direction parallel to the Y-axis direction |
v _Y | (= ι _Y · d θ _Y / dt) will move simultaneously. Here, the velocities v _X 'and v _Y are velocity vectors, and | v _X ' | and | v _Y | are their magnitudes. Therefore, as shown in FIG. 7A, the Young's fringe has the velocity vector v
It will move in _X 'and v _Y vector sum is a velocity vector v _XY of. The velocity vector v _XY is expressed by the following mathematical formula 15.
Given in. That is, the Young fringes move at the speed | v _XY | in the direction of the speed vector v _XY which is a direction oblique to the directions of the X axis and the Y axis. It should be noted that FIG. 7A shows that the Young fringe bright line located at the position indicated by the dotted line has moved to the position indicated by the solid line at the speed | v _XY |.

[0070]

[Formula 15] v _XY = v _X '+ v _Y

The arithmetic / control unit 14 is the deflector driver 1
The sweep speeds df _X '/ dt and df _Y / dt are controlled via 5, and two or more output peaks of the photodiode 13 are present in the display surface 14A of the device 14 (within the time limit range T _{max of the} device 14). To be displayed. The arithmetic and control unit 14 also controls the deflector driver 15 so that the output peak time interval becomes equal to or more than the minimum limit value T _{min of the} unit 14. In this way, the output peak time interval ΔT _XY
To measure.

As shown in FIG. 7B, the Young fringes have a movement vector A _X 'in the direction parallel to the X axis and a movement vector A _{Y in the} direction parallel to the Y axis during the output peak time interval ΔT _XY.
Move simultaneously, and as a result, move vector A _XY (= A) which is the vector sum of these move vectors A _X 'and A _Y
Move only _X '+ A _Y ). This movement vector A _xY has a movement direction (the velocity vector v
_XY direction) and its length is equal to the distance between the bright lines of the Young fringes in that direction. Here, the length | A _X '| of the movement vector A _X ' is given by the following formula 16.
In addition, the length | A _Y | of the movement vector A _Y is obtained by Expression 17.

[0073]

[Number 16] _{| A X '| = v X} ' · ΔT XY = ΔT XY · ι X · dθ X '/ dt = ΔT XY · ι X · (d f X' / dt) · (λ 0 / nv)

[0074]

[Expression 17] | A _Y | = v _Y · ΔT _XY = ΔT _XY · ι _Y · dθ _Y / dt = ΔT _XY · ι _Y · (df _Y / d t) · (λ ₀ / nv)

[0075] As further shown in FIG. 7B, the movement vector A _XY length | A _XY | by the following equation 18, also parallel to the X axis of the movement vector A _XY as the direction of the movement vector A _XY The angle γ with respect to

[0076]

[Formula 18] | A _XY | ² = | A _X '| ² + | A _Y | ²

[0077]

Γ = tan ⁻¹ (| A _Y | / | A _X '|)

From the above equations 16 to 19, the distance between the bright lines of the Young fringes | A _XY | in the moving direction of the Young fringes and the angle γ of the moving direction with respect to the X-axis direction are obtained.

The fringe spacing of the Young fringes (that is, the distance between the bright lines of the Young fringes in the direction perpendicular to the Young fringes) ΔL and the fringe direction (direction perpendicular to the fringes) are the Young fringes in the moving direction of the obtained Young fringes. The distance between bright lines | A _XY | and the moving direction angle γ are obtained as follows.

For example, as shown in FIG. 7B, it is assumed that as a result of the Young fringes moving by the movement vector A _XY , the point O on the bright line of the Young fringes moves to the point O'as shown in FIG. The movement vector length | _AX ′ |, the movement vector length |
A _Y |, the Young fringe movement direction angle γ, and the Young fringe bright line distance | A _XY | in the movement direction are obtained from the above-described formulas 16 to 19. The Young fringe spacing ΔL _X in the direction parallel to the X-axis direction has already been measured.
Therefore, the distance B in FIG. 8 is given by the following formula 20. As a result, the Young fringe spacing ΔL (the distance between the Young fringe bright lines in the direction perpendicular to the Young fringes) is calculated by the mathematical expression 21.

[0081]

[Formula 20] B ² = | A _XY | ² + (ΔL _X ) ² −2 | A _XY | · ΔL _X · cos γ

[0082]

ΔL = 2 [s (s−ΔL _X ) (s− | A _XY |) (s−B)] ^1/2 / B

In the equation 21, s satisfies the following equation 22.

[0084]

[Equation 22] 2s = ΔL _X + | A _XY | + B

Considering the angle ψ with respect to the direction parallel to the X-axis direction as the direction of the Young fringe (direction perpendicular to the Young fringe), the angle ψ is given by the following formula 23.

[0086]

Ψ = 90 ° −sin ⁻¹ [(| A _XY | / B) sin γ]

By the arithmetic / control unit 14 performing these calculations, the fringe spacing ΔL of the Young fringes and the fringe direction ψ are obtained. Therefore, the measured object 19
Is calculated. Further, the stripe direction ψ indicates the moving direction of the measurement object 19 with respect to the direction parallel to the X-axis direction.

The present invention is not limited to the optical displacement measuring device of the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the Y-axis direction is deflected after the X-axis direction is deflected, but the reverse is also possible. Also, in the above embodiment,
The two deflectors 12X and 12Y are arranged so that their deflection directions (X-axis direction and Y-axis direction) are at right angles to each other, but they may not be at right angles. It suffices if the Young fringes can be deflected in at least two different directions by arranging them so that the deflection directions are not parallel and have some angle. In addition,
When the deflectors 12X and 12Y are arranged so that their deflection directions (that is, the X-axis and the Y-axis) form a certain angle α, for example, instead of the half-wave plate 11, the polarization state is the same angle α.
An element having a function of rotating only is arranged between the deflectors. This is because it is necessary to make the deflection characteristics in the two deflection directions the same.

In the above embodiment, the acousto-optic deflector is used as a means for deflecting the Young fringes in at least two different directions, but the deflecting means is not limited to this. For example, a galvanometer mirror may be used, an electro-optical deflector,
A magneto-optical deflector or the like may be used.

In the above embodiment, the photodiode 1 is used as means for detecting the changing state (moving state) of the Young's fringes.
Although 3 was used, it is not limited to this. Any one-dimensional optical detector capable of measuring the light intensity and its change at a position on the Fourier transform surface (focal plane after the Fourier transform lens) may be used. Further, it is not limited to such a point light detector as long as it can detect a state in which Young fringes formed on the Fourier transform surface (focal plane after the Fourier transform lens) change.

In the above-mentioned embodiment, the optical displacement measuring device is fixed and the measuring object is moved, but the reverse is also possible. That is, the optical displacement amount measuring device may be moving and the measuring object may be fixed. In this case, the absolute movement amount and movement direction of the optical displacement amount measuring device are obtained by measuring the movement amount and movement direction of the fixed measuring object relative to the optical displacement amount measuring device. . For example, by mounting the optical displacement amount measuring device on a moving object such as an automobile, the moving amount and speed of this moving object can be obtained.

Further, the measurement object may be irradiated with incoherent light instead of coherent light such as laser light. In this case, not the speckle pattern but the image of the measuring object is recorded in the light modulator. In this way, the image of the object before and after the displacement is double recorded on the optical modulator. The recorded images of the object before and after the displacement are read out by coherent light and Fourier-transformed to form Young fringes. This is deflected in two directions by the deflector. By measuring this deflection result, the displacement amount and displacement direction of the measurement object can be obtained.

The means for double recording the speckle pattern is not limited to the ferroelectric liquid crystal spatial light modulator.
Any spatial light modulator capable of accumulating the light receiving pattern before displacement of the measurement object at least until recording the light receiving pattern after displacement and capable of double recording the images before and after the object displacement is sufficient.
For example, a photographic plate may be used.

Further, in the above-described embodiment, the object is irradiated with light and the displacement amount and displacement direction of the object are measured by the reflected light pattern thereof. However, depending on the kind of the measured object and the like, the transmitted light pattern may be measured. May be. That is, the image and the speckle pattern formed on the transmitted light of the measurement object may be double recorded on the optical modulator.

When the light intensity of the pattern formed in the transmitted light or the reflected light from the measurement object is small, a known image intensifier is provided between the imaging lens 5 and the light modulator 6, and the pattern is formed. It is also possible to make the light incident on the writing incident surface 6S _w of the optical modulator 6 after increasing the light intensity.

In the above-mentioned embodiment, a part of the light from the He-Ne laser device 2 is deflected by the deflector 4 and irradiated on the measurement object 19 to form a speckle pattern. However, the deflector 4 may not be provided, and the light from the He-Ne laser device 2 may be constantly applied to the measurement object 19. In this case, at a certain time t, there is a time interval Δt of 2
The speckle pattern is double-recorded by applying the write drive voltage V _w to the optical modulator 6. Also, H
A laser diode (LD) that is a pulsed light source may be provided separately from the e-Ne laser device 2 to selectively irradiate the measurement object 19 with pulsed LD light to form a speckle pattern.

[0097]

As is apparent from the above detailed description, in the optical displacement measuring device of the present invention, the object to be measured, which is relatively displaced with respect to the device, is irradiated with the light by the light irradiating means and measured. The recording means receives the transmitted light or the reflected light from the object. The recording means double-records the image of the measuring object at a predetermined time interval, and records the relative displacement state of the measuring object and the recording means (device). The recording means is irradiated with coherent light from the coherent light projecting means to read out the double recorded image of the recording means. The read double recorded image is deflected by at least two different directions by the deflecting means. At the same time, the read double recording image is Fourier transformed by the Fourier transforming means to form Young fringes which are Fourier transformed images. Therefore, the formed Young fringes move in two different directions based on the deflection of the read double recording image. By detecting the change (movement) state of the Young fringes due to the movement in the two directions, the fringe direction and the fringe spacing of the Young fringes are calculated. Based on this calculation result, the relative displacement amount and displacement direction of the measurement target optical displacement amount measuring device are calculated. According to the present invention,
Move the Young fringes in at least two different directions,
The moving state (changed state) is detected and the fringe direction and fringe spacing of the Young fringes are calculated. Therefore, data acquisition and complicated comparison calculation are not required to obtain the fringe direction and the fringe spacing of the Young fringes, so that the measurement can be performed in a short time and the real-time measurable property is excellent.

Further, since it is sufficient to have a deflector for deflecting Young fringes, which are Fourier transform images, in at least two directions different from each other, it is possible to downsize the entire apparatus.

[Brief description of drawings]

FIG. 1 is an optical system diagram showing an optical displacement amount measuring device according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing an optical modulator used in the present invention.

FIG. 3 is an operation timing chart of the optical displacement amount measuring device according to the embodiment of the present invention.

FIG. 4A is a sectional view for explaining an acousto-optic deflector used in the present invention.

FIG. 4B is a perspective view for explaining how the light from the lens 10 is deflected in two different directions in the present invention.

FIG. 4C is a perspective view illustrating an arrangement state of two acousto-optic deflectors and a half-wave plate according to the present invention.

FIG. 4D is a view for explaining the position of the photodiode 13 with respect to the deflectors 12X and 12Y in the present invention,
It is a front view seen from the lens 10.

FIG. 5A is an explanatory diagram for explaining how Young fringes are deflected by a deflector 12X in the present invention.

FIG. 5B is a diagram for explaining how the received light intensity of the photodiode 13 temporally changes as a result of Young fringes being deflected by the deflector 12X in the present invention.

FIG. 5C is an explanatory diagram for explaining how Young fringes are deflected by the deflector 12Y in the present invention.

FIG. 5D is a diagram illustrating how the received light intensity of the photodiode 13 changes with time as a result of Young fringes being deflected by the deflector 12Y in the present invention.

FIG. 6 is a diagram illustrating a method of calculating a fringe interval and a fringe direction of Young fringes.

FIG. 7A is an explanatory diagram for explaining how Young fringes are deflected by deflectors 12X and 12Y in the present invention.

FIG. 7B is an explanatory diagram illustrating a state in which Young fringes move during a time interval ΔT _XY .

FIG. 8 is a diagram illustrating a method of calculating a fringe interval and a fringe direction of Young fringes.

[Explanation of symbols]

 1 Optical displacement amount measuring device 2 He-Ne laser device 3 Half mirror 4 Acousto-optical deflector 6 Optical modulator 10 Fourier transform lens 11 Half-wave plate 12X Acousto-optical deflector 12Y Acousto-optical deflector 14 Arithmetic / control device 15 Deflection Driver 16 Optical modulator controller 17 Deflector controller 19 Measuring object

Claims (2)

[Claims] 1. A light irradiating means for irradiating light to an object to be measured, and reflected light or transmitted light from the object to be measured based on the irradiation light is received to form an image of the object to be measured at predetermined time intervals. Recording means for recording and recording the relative displacement of the measurement object, reading coherent light projecting means for irradiating the recording means with coherent light to read the recorded image, and the read image Deflection means for deflecting at least two directions different from each other, Fourier transformation means for Fourier transforming the read-out image, change state of the Fourier-transformed image due to deflection of the read-out image, the recording means, and the recording means. An optical displacement amount measuring device, comprising: a detecting unit for obtaining a relative displacement amount with respect to the optical displacement amount measuring device. 2. The light irradiating unit irradiates the measurement target with coherent light to form a speckle pattern on reflected light or transmitted light from the measurement target, and the speckle pattern is duplicated on the recording unit. The optical displacement amount measuring device according to claim 1, wherein the optical displacement amount is recorded.